The present invention is directed to a test tool for a nuclear reactor vessel level instrumentation system and, more particularly, the present invention is directed to a test tool for a computer controlled instrumentation system which measures fluid level in a pressurized water nuclear reactor and compensates for changes in measured values of core coolant fluid level due to fluid temperature changes, fluid pressure changes caused by core coolant pump operation, coolant outlet temperature changes, and core coolant inlet pressure changes to obtain an actual fluid level.
The present invention interfaces with the reactor vessel level instrumentation system (RVLIS) 10 of FIG. 1 at the electrical field line terminal blocks and substitutes for or simulates various signals supplied by the fluid level monitoring system. The RVLIS equipment 10 is arranged in two identical, redundant systems; however, only one system is illustrated in FIG. 1. Each system 10 receives inputs from differential pressure cells 11-13, hydraulic isolators 14-16, resistance temperature detectors 17-23, pump status monitors 24, a wide range pressure sensor 25 and temperature hot sensors 26, and includes subsystems for sampling the various input signals and converting the values sampled into vessel fluid level using steam tables. An 8-bit or 16 bit microcomputer processing unit in the system 10 converts all the inputs into the vessel level and displays the level for plant operators.
Capillary fluid impulse lines extend through containment wall 27 to the hydraulic isolators 14-16. The hydraulic isolators 14-16 provide hydraulic coupling, isolation of lines, and limit switch inputs to instrumentation system 10 when the isolators 14-16 are overranged, that is, experiencing too much pressure. When the isolators 14-16 are overranged, the system measurements will be in error. The differential pressure cells 11-13 measure the difference in fluid height between reference lines subject to system pressure, through the hydraulic isolators 14-16, located outside the containment wall and the fluid level in the reactor vessel 28. The impulse lines inside the containment wall 27 will be exposed to temperature increases which change the fluid density which must be taken into account in vessel level determination. Strap-on resistance temperature detectors 17-23 are located on each vertical run of separately routed impulse lines to determine the impulse line temperature. This temperature is used to correct the reference leg density contribution to the differential pressure measurement. That is, when temperature in the impulse lines changes, the density of the water changes, changing the height of water measured by cells 11-13. Changes in liquid density thus require changes in compensation for the differential pressure cell outputs. Another factor affecting reactor fluid level measurement is the status of reactor coolant pumps 29. Whenever the pumps 29 are on the differential pressure in the reactor vessel 28 is higher than when off, therefore, pump status across the core is provided by pump status monitors 24 to allow calculation of actual reactor fluid level. Depending upon which of four possible coolant pumps 29 are operating, the coolant differential pressure across the core varies which also varies the indicated fluid level within the vessel. The differential pressure across the core is measured by the wide range pressure sensor 25. Another factor that must be considered when calculating vessel fluid level is coolant fluid outlet temperature which is measured by temperature hot sensors 26. Whenever coolant temperature is high coolant density is low and the output of the differential pressure cells 11-13 must be compensated therefor.
The 8 or 16 bit microprocessor within the RVLIS 10 samples the various sensors discussed above and displays vessel liquid level on a remote display 30 that is viewed by plant operators. The system 10 also includes a local display 31 which is used by maintenance technicians to test the system. The local display 31 is capable of not only displaying reactor vessel fluid level, but all of the various input signals used to calculate the fluid level. The reactor vessel level instrumentation system 10 of FIG. 1 can be purchased from Westinghouse Electric Corporation. The 8-bit microcomputer based system is called the RVLIS while the 16 bit microcomputer based system is called the RVLIS-86.
Prior to the present invention, dummy inputs were supplied to the RVLIS by using edge connectors on the various circuit boards which bypassed all interface circuits and analog-to-digital converters.